The present invention generally relates to a film forming apparatus for use in a semiconductor-producing process and a method for producing a barrier film to be used in a semiconductor.
In the process for producing Cu wirings to be used in semiconductor devices, the film forming temperature is limited to 300 degree Celsius or less. This is the reason why when the film forming temperature is not less than 300 degrees Celsius, a phenomenon so-called stress migration (SM) occurs to the Cu wiring so that the reliability of the Cu wirings is conspicuously deteriorated.
In a conventional art, a method is carried out in which an easily pyrolyzable MO-based material is used as a metallic material gas because of that temperature limitation, and a barrier metal is obtained at 300 degrees Celsius or less by reacting it with a plasmatized reactive gas.
However, since the barrier metal obtained by this method includes many impurities (such as, C and O), only film having high specific resistance (a few hundred to several thousand μ Ω cm) can be obtained. Further, since many impurities are contained, there is a problem in that adhesion between the barrier film and a Cu film as an upper layer is low. When the adhesion is low in a Cu process, the film is peeled in a CMP step, thereby resulting in a fatal defect.
This is caused by C and O being contained in a gas of an MO-based metallic material (such as, PDMAT, TDMAT) so that if a gas of an inorganic metallic material (TiCl4 or WF6) is used, a barrier film containing no impurities is obtained. However, there is a problem in that the gases of the inorganic metallic materials have high pyrolysis temperatures of 400 degrees Celsius or more.
When a reactive gas is plasmatized and is reacted with a gas of a metallic material, the plasma does not easily enter pores having high aspect ratio, so that even if a low-resistance film is formed on a surface of a substrate, the reaction between the metallic material gas and the plasma of the reactive gas does not proceed at the bottom face of the pore having the high-aspect ratio because the plasma of the reactive gas does not easily enter the high-aspect pores. Consequently, only the barrier films having small film thicknesses on the bottom faces could be obtained. Such barrier film has poor coverage.
On the other hand, according to an ALD method, a reaction can be carried out without using plasma. For example, according to the ALD method, tungsten nitride and titanium nitride can be obtained according to the following formulae:(1) WF6+2NH3→N+6HF+N2   (1)(2) TiCl4+8/6NH3→TiN+4HCl+1/6N2.
However, although the above reactions occur at 400 degrees Celsius or more, the reaction does not almost proceed at 300 degrees Celsius or less. Thus, only film having extremely high resistance (a few thousand to tens thousand .mu..OMEGA.cm) can be obtained in the case of the inorganic materials.
If radicals of the reactive gas are produced instead of the plasma, the radicals can enter the pore, so that a barrier film having good coverage can be formed. However, there is a problem in that a reaction product is deposited on a surface of a catalytic material, and the catalytic material must be frequently cleaned. These problems are disclosed in JPA 2005-158761 and JPA 2006-28572.